Juvenile ceroid-lipofuscinosis is a progressive neurodegenerative disease caused by mutations in the CLN3 gene. Because CLN3 is a transmembrane protein, it is not likely to be treatable by a protein replacement therapy. Gene therapy, therefore, is the best hope for treating Juvenile cerold-lipofuscinosis at this time. We will use a c1n3-knockout mouse model developed by Dr. Martin Katz to test the feasibility of treating Juvenile ceroid-lipofuscinosis using AAV gene therapy vectors. To prevent neuronal cell death in juvenile cerold lipofuscinosis and many other neurological disorders, we need to transduce as many cells as possible in the central nervous system. This requires increasing both the number and types of cells transduced by current AAV2 vectors. We will approach this problem in two ways. First, by using a different serotype of AAV (AAV5) that binds to a different cellular receptor, we hope to transduce cells that are resistant to transduction by AAV2. Second, by isolating mutants in the AAV2 capsid that bind heparin at a lower affinity than wild type AAV2, we hope to increase the diffusion of the vector away from the injection site and therefore, increase the number of cells transduced. We will use transduction of the mouse retina to optimize our AAV vectors, because it is easily accessible and because it is an immune privileged site, which allows long-term expression of foreign proteins such as NLS-GFP. We will use a vector that expresses both CLN3 and NLS GFP, which will serve as a marker for transduced cells, to transduce neuronal cells in the retinas of cln3 knockout mice. We will monitor the success of therapy in three ways. First, cells that lack CLN3 accumulate an autofluorescent pigment in lysosomal storage bodies. Therefore, transduced cells that express CLN3 and NLS-GFP should no longer accumulate this autofluorescent pigment. Second, the expression of CLN3 :) should prevent neuronal cell death in the retina. Loss of neurons will be assessed microscopically. Third, the function of the retina can be determined over time by a non-invasive ERG.